James K. Knowles Lecture & Caltech Solid Mechanics Symposium

Ten Years of Progress in Nanoscale Mechanical Experimentation

Horacio D. Espinosa, James and Nancy Farley Professor of Mechanical Engineering, Northwestern University

In the past decade, there has been a major thrust to develop novel nanomaterials exhibiting unique mechanical and electro-mechanical (e.g., piezoelectric) properties. These nanomaterials are envisioned as building blocks for the next generation of lightweight materials, electronics, sensors, and energy harvesting systems. In these applications, identification of size dependent mechanical, thermal, and electrical properties of 1D and 2D materials is essential. Such endeavor has proven challenging from both experimental and modeling perspectives. In this presentation, progress in nanoscale mechanical experimentation towards accurate identification of nanomaterial properties and bottom up design of nanomaterials will be discussed. As an example of nanomaterial property identification, we will explore the use of microelectromechanical systems (MEMS) for in situ electron microscopy testing of low dimensional nanomaterials. We will examine mechanical properties of silver nanowires as a function of size and deformation rate. Based on the experimental findings, we will formulate molecular models to interpret observed deformation mechanisms and defect kinetics. Furthermore, the validity of force fields commonly used to model metallic nanowires will be examined through one-to-one comparison between experimental measurements and atomistic simulations. In a second example, we will discuss the use of nanomechanical experimentation to build computational models for bottom up design of nanomaterials. We will examine bio-inspired graphene oxide polymer composites and show a methodology for characterization and model parametrization of constituents from graphene oxide flakes, with different degrees of oxidation, to the selection of polymer interfaces for optimal material toughness, stiffness, and strength.